<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        html {
            font-size: 100px;
        }
        div {
            background-color: aqua;
            margin-top: 10px;
            font-size: 0.6rem;
        }
        p:nth-child(1){
            font-size: 0.2rem;
        }
        p:nth-child(2){
            font-size: 0.3rem;
        }
        p:nth-child(3){
            font-size: 0.4rem;
        }
    </style>
</head>
<body>
    <p>rem 1</p>
    <p>rem 2</p>
    <p>rem 3</p>

    <div>
        this is div1
    </div>
</body>
</html>